Method for producing multilayer coatings

ABSTRACT

The invention relates to a process for applying a multicoat finish to a substrate surface, comprising the following steps:(1): applying an aqueous basecoat A to the substrate surface,(2): forming a polymer film from the aqueous basecoat A applied in stage (1),(3): applying an aqueous transparent topcoat B to the basecoat film obtained in stage (2), and finally(4); baking the basecoat film and the topcoat film together,wherein the basecoat A comprises at least one hydroxyl-containing binder in aqueous solution or dispersion and a stable aqueous dispersion, prepared with a hydroxyl-containing emulsifier, of a hydrophobicized amino resin, and to substrates coated in accordance with the process of the invention.

FIELD OF THE INVENTION

The invention relates to a process for producing a multicoat finish on asubstrate surface by successive application of an aqueous basecoat andof an aqueous topcoat and the subsequent simultaneous baking of thebasecoat film and of the topcoat film, said aqueous basecoat comprisinghydrophobicized amino resins emulsified with hydroxyl-containingemulsifiers.

BACKGROUND AND SUMMARY OF THE INVENTION

In automotive finishing in particular, though also in other sectorswhere there is a desire for coatings having a good decorative effect andat the same time affording good protection against corrosion, it isknown to provide substrates with two or more coating films arranged atopone another.

Multicoat paint systems are preferably applied in accordance with theso-called basecoat/clearcoat process; that is, a pigmented basecoat isapplied first and following a short flash-off time without a baking step(wet-on-wet technique) is coated over with a clearcoat. Subsequently,basecoat and clearcoat are baked together. The basecoat/clearcoatprocess has acquired particular importance in connection with theapplication of automotive topcoats, especially in the case of metallicpaints.

Economic and environmental considerations have resulted in attempts touse aqueous basecoats for the production of multicoat finishes.

The coating compositions for producing these basecoat films must be ableto be processed by the nowadays customary, rational wet-on-wettechnique; that is, following a short initial drying period without abaking step, they must be overcoated with a transparent topcoat filmwithout exhibiting disruptive etching and “strike-in” phenomena.

DE-A-40 28 386 describes a process for producing a multicoat finish on asubstrate surface, in which (1) as the basecoat, a water-thinnablebasecoat is applied which comprises water, organic solvents if desired,a water-dilutable binder, pigment particles, and a polyamide asTheological assistant, (2) a polymer film is formed on the surface fromthe composition applied in stage (1), (3) a suitable transparent topcoatis applied to the resulting basecoat film, and subsequently (4) thebasecoat film is baked together with the topcoat film. As the topcoat itis possible to use conventional solventborne clearcoats, water-thinnableclearcoats, or transparent powder coating materials.

DE-A-42 16 613 embraces a process for producing a two-coat paint systemon a substrate surface, in which (1) a pigmented aqueous basecoatcomprising as its binder a water-dilutable (meth)acrylate emulsionpolymer prepared in the presence of specific emulsifiers is applied tothe substrate surface, (2) a polymer film is formed from the basecoatapplied in stage (1), (3) a transparent topcoat is applied to theresulting film, and subsequently basecoat film and topcoat film arebaked together. As the topcoats, it is again possible to useconventional solventborne clearcoats, aqueous clearcoats, or transparentpowder coating materials.

In the case where aqueous basecoats, in accordance, for example, withDE-A-40 28 386 or DE-A-42 16 613, are used simultaneously with aqueoustopcoats in the basecoat/clearcoat process (wet-on-wet technique) greatproblems occur, especially when using aqueous slurries of transparentpowder coating material as the topcoat, since the aqueous basecoatfilms, which have undergone only initial drying for a short period, whencoated with the aqueous topcoat withdraw water from it and arethemselves in turn partially dissolved. As a consequence of the partialdissolution of the aqueous basecoat film and of the attendant filmsoftening, and as a consequence of the withdrawal of water from thedrying aqueous topcoat, the initial drying and baking of thebasecoat/topcoat system are accompanied by cracks over the entiresurface—a phenomenon also known as “mud cracking”. A further severeproblem is the tendency of aqueous basecoats toward popping in thecourse of baking.

DE-A-42 22 194 describes a process for producing two-coat paint systemson a substrate surface, in which (1) a pigmented, solvent- or waterbornebasecoat is applied to the substrate surface, (2) a polymer film isformed from the paint applied in stage (1), (3) a transparent powdertopcoat is applied to the resulting basecoat film, said topcoatcomprising an epoxy-functional polyacrylate resin as its binder, andsubsequently (4) the basecoat film is baked together with thetransparent powder coating film.

A fundamental problem of DE-A-42 22 194 is the need for differentapplication methods for the basecoat, which is generally applied byspraying or dipping, and for the transparent powder coating material,which is generally applied by means of electrostatic techniques.Furthermore, DE-A-42 22 194 allows solventborne basecoats, which againis objectionable from the environmental standpoint.

The object of the present invention, therefore, was to provide suitablebasecoat compositions with which processes for multicoat finishing inaccordance with the so-called basecoat/clearcoat process using thewet-on-wet technique, in which both basecoat and topcoat are aqueoussystems and can be applied to the substrate using the same applicationmethod, can be conducted in such a way that the partial dissolution ofthe aqueous basecoat film and the attendant film softening by theaqueous topcoat play a minor part, that no cracks appear in thebasecoat/topcoat system (mud cracking) in the course of initial dryingand/or in the course of baking, and, in particular, that the tendencytoward popping in the basecoat film during the baking step is reduced.

The invention accordingly provides a process for producing a multicoatprotective and/or decorative finish on a substrate surface, comprisingthe following steps:

(1): applying an aqueous basecoat A, comprising a hydrophobicized aminoresin as crosslinker, said amino resin being stably emulsified in theaqueous phase by means of a hydroxyl-containing emulsifier, andcomprising at least one hydroxyl-containing binder present in aqueoussolution or in aqueous emulsion, to the substrate surface,

(2): forming a polymer film from the aqueous basecoat A applied in stage(1),

(3): applying an aqueous transparent topcoat B to the resulting basecoatfilm, and finally

(4): baking the basecoat film and the topcoat film together.

In one preferred embodiment of the invention the hydroxyl-containingemulsifier for the hydrophobic amino resin, which is preferably amelamine-formaldehyde condensate etherified with C3 to C12 alcohols, isan oligomeric and/or polymeric diol and/or polyol having an emulsifyingaction, with particular preference a diol and/or polyol from the groupconsisting of polyacrylate diols and/or -polyols, polyesterdiols and/or-polyols and polyetherdiols and/or -polyols, and, with very particularpreference, from the group consisting of polyurethanediols and/or-polyols and polycarbonatediols and/or -polyols.

The hydroxyl-containing binder in the basecoat A is preferably selectedfrom the group consisting of polyacrylates, polyurethanes, polyesters,polyethers, alkyd resins and cellulose derivatives.

In a further preferred embodiment of the invention the aqueous topcoat Bis an aqueous one-component and/or two-component clearcoat or, withparticular preference, a powder slurry clearcoat.

DETAILED DESCRIPTION OF THE INVENTION

The Basecoat A

In accordance with the invention, the basecoat A comprises, as thecrosslinking agents, hydrophobicized amino resins emulsified stably inthe aqueous phase by means of hydroxyl-containing emulsifiers.

The hydrophobic amino resins, which are known per se, are preferablycondensates of aldehydes, especially formaldehyde, and, for example,urea, guanamine, benzoguanamine, and preferably melamine.

The hydrophobic amino resins contain alcohol groups, preferably methylolgroups, which are etherified preferably with C3 to C12 alcohols,examples being isopropanol, n-butanol, isobutanol, tert-butanol, amylalcohol, 1-hexanol, 1-octanol, 2-ethylhexanol, 1-decanol, isodecanol,1-dodecanol and isododecanol.

Butanol-etherified melamine-formaldehyde resins are used in particularas the hydrophobic amino resins.

As the hydroxyl-containing emulsifiers for the hydrophobic amino resinsit is preferred to use diols and/or polyols having emulsifyingproperties, with particular preference diols and/or polyols having amolecular weight of between 500 and 50,000 daltons, and, with veryparticular preference, having a molecular weight of between 500 arid5000 daltons.

The emulsifying diols and/or polyols are preferably selected from thegroup consisting of polyacrylatediols and/or -polyols, polyesterdiolsand/or -polyols and polyetherdiols and/or -polyols, and, with veryparticular preference, from the group consisting of polyurethanediolsand/or -polyols and polycarbonatediols and/or -polyols.

The ratio of hydrophilic to hydrophobic moieties in the diols and/orpolyols is established preferably either by way of the molecular weightof the diols and/or polyols and the proportion of hydrophilic groupsalready present in the diol and/or polyol, or by way of the introductionof additional hydrophilic groups, such as, for example, acid groups orsalts thereof, e.g., carboxyl or carboxylate groups, sulfonic acid orsulfonate groups, and phosphonic acid or phosphonate groups.

Further crosslinking agents which may be present in the basecoat A areany crosslinking agents suitable for the crosslinking ofhydroxyl-containing binders.

Preferred further crosslinking agents are blocked and/or nonblockedpolyisocyanates whose isocyanate groups are attached preferably toaliphatic or cycloaliphatic radicals. Examples of such polyisocyanatesare hexamethylene diisocyanate, isophorone diisocyanate,trimethylhexamethylene diisocyanate, dicyclohexylmethane diisocyanate,1,3-bis(2-isocyanatoprop-2-yl)benzene, and also adducts of thesepolyisocyanates with polyols, especially low molecular mass polyols,such as trimethylolpropane, for example, and also polyisocyanates whichare derived from the aforementioned polyisocyanates and containisocyanurate and/or biuret groups, and which preferably contain morethan two isocyanate groups in the molecule.

For the blocking of the polyisocyanates it is possible to use anyblocking agent which is known per se to the skilled worker and has asufficiently low deblocking temperature.

Hydroxyl-containing binders used in the basecoats A are preferablyaqueous dispersions of preferably hydroxyl-containing polyacrylates,polyurethanes, polyesters, poly-ethers, alkyd resins and/or cellulosederivatives. Suitable aqueous binders based on hydroxyl-containingpolyacrylates are described, for example, in DE-A-38 32 826, whichdiscloses a two-stage preparation process for water-dilutablepolyacrylates that are suitable for use in basecoats.

Hydroxyl-containing polyurethanes for aqueous basecoats A are disclosed,for example, in DE-A-38 25 278, in which the polyurethanes from amixture of polyetherdiols and polyesterdiols, diisocyanates andcompounds having at least two isocyanate-reactive groups and one groupcapable of forming anions are reacted to give an intermediate which issubsequently reacted with polyols containing at least three hydroxylgroups.

Hydroxyl-containing polyesters and/or polyethers suitable as binders foraqueous basecoats A, and also capable of being employed as prepolymersin the synthesis of the hydroxyl-containing polyurethanes, are likewisedescribed in the prior art.

The use of alkyd resins and cellulose derivatives as binder componentsin aqueous basecoats is disclosed, for example, in DE-A-39 22 363.

Preferred binders are acrylated polyurethane resins, obtainable, forexample, in accordance with DE-A-43 39 870, by subjecting anethylenically unsaturated monomer or a mixture of ethylenicallyunsaturated monomers to free-radical polymerization in an aqueousdispersion of a polyurethane resin, the weight ratio between thepolyurethane resin and the ethylenically unsaturated monomer beingbetween 1:10 and 10:1.

In addition to the hydroxyl-containing binders described above, thebasecoats A used in accordance with the invention may also include, inproportions of up to 75% by weight, based on the binder, further bindercomponents having low hydroxyl contents or being free from hydroxylgroups, such as, for example, water-dilutable polyester resins,water-dilutable polyacrylate resins, water-dilutable polyurethaneresins, water-dilutable alkyd resins, water-dilutable cellulosederivatives, and water-dilutable polyether resins.

As pigments, the basecoats A include, if desired, any organic orinorganic pigments suitable for aqueous coating materials, or mixturesof such pigments, in proportions of up to 30% by weight, preferablybetween 5 and 25% by weight, based on the solids content of thebasecoat. Examples that may be mentioned of pigments which can be usedare titanium dioxide, iron oxide, carbon black, metal pigments,especially aluminum pigments, and pearl luster or interference pigments.

The basecoats A preferably comprise metal pigments, especially aluminumpigments, alone or in combination with nonmetallic pigments.

It is also possible for anticorrosion pigments to be present, such aszinc phosphate, for example.

In addition, the basecoat A may also include fillers known per se andcustomary for coating materials, examples being silica, magnesiumsilicate, titanium dioxide, and barium sulfate.

Furthermore, the basecoats A of the invention may include crosslinkedpolymeric microparticles (compare, for example, EP-A-0 038 127) and/orcustomary organic or inorganic rheology-controlling additives. Examplesof compounds which act as thickeners are sheet silicates orwater-soluble cellulose ethers and also synthetic polymers having ionicor associative groups, such as polyvinyl alcohol, polyamides,poly(meth)acrylamide, poly(meth)acrylic acid, polyvinyl-pyrrolidone, orhydrophobically modified ethoxylated urethanes or polyacrylates.

The basecoats A may also contain organic solvents in amounts of up to15% by weight. Examples of suitable organic solvents are naphthalenes,mineral spirits or alcohols, preferably low molecular mass diols, suchas alkylene glycols or dimethylolcyclohexane, for example.

Further components which may be present in the basecoats A comprisefilm-forming auxiliaries, such as, for example, dicarboxylic aciddialkyl esters or high-boiling mineral spirits or naphthalenes, having aboiling point of more than 100 degrees C, preferably more than 140degrees C.

The basecoats A of the invention may additionally comprise furtherauxiliaries and/or additives, such as, for example, catalysts for thecrosslinking reaction, defoamers, dispersing auxiliaries, wettingagents, preferably carboxy-functional dispersants differing from theabovementioned emulsifiers, antioxidants, UV absorbers, free-radicalscavengers, leveling assistants, and/or biocides.

The Topcoat B and the Process of the Invention

Topcoats B which can be used are all aqueous topcoats suitable for theproduction of two-coat paint systems. The topcoats B are preferablyaqueous clearcoats or aqueous coating materials comprising transparentpigments. The aqueous clearcoats B can be one-component or two-componentclearcoats, particular preference being given to powder slurryclearcoats.

Exemplary of suitable topcoats B are aqueous topcoats in accordance withDE-A-38 32 826, having hydroxyl-containing water-dilutable polyacrylateresins as binders and conventional amino resins as crosslinking agents(two-component clearcoat).

The powder slurry clearcoats which are particularly preferred astopcoats B consist preferably of a powderous component comprising atleast one binder, preferably a crosslinking agent and, if desired,catalysts for the crosslinking reaction, and also auxiliaries andadditives typical of powder coatings, such as, for example,devolatilizing agents, leveling agents, UV absorbers, free-radicalscavengers or antioxidants, and of an aqueous dispersion as mixercomponent, comprising a thickener alone or together with dispersants,small amounts of solvent, biocides and further auxiliaries, such aswetting agents, defoamers, and also additional leveling agents, UVabsorbers, free-radical scavengers or antioxidants, for example.

Powder slurry clearcoats of this kind are described, for example, inU.S. Pat. No. 4,268,542.

The process for applying multicoat finishes using the basecoats of theinvention is subdivided into the following stages:

(1): applying an aqueous basecoat A to the substrate surface,

(2): forming a polymer film from the aqueous basecoat A applied in stage(1),

(3): applying an aqueous transparent topcoat B to the basecoat filmobtained in stage (2), and finally

(4): baking the basecoat film and the topcoat film together.

In order to form the polymer film in accordance with stage (2), thebasecoat film applied in stage (1) is left to evaporate, preferably atelevated temperature, before the application of the transparent topcoatB in stage (3), the evaporation time depending on the temperature andbeing adjustable over wide ranges. For example, at temperatures of from60 to 100 degrees C, preferably from 70 to 85 degrees C, evaporationtimes of from 1 to 15 minutes, preferably from 4 to 10 minutes, arechosen.

The basecoat A and the topcoat B are applied by conventional methodswhich are known in the prior art. The dry film thickness of the basecoatfilm is between 10 and 40 μm, preferably between 12 and 25 μm, and thedry film thickness of the topcoat film is between 20 and 60 μm,preferably between 35 and 45 μm. Following application of the topcoat Bin stage (3) and prior to the baking step in stage (4), the basecoatfilm and the topcoat film are preferably dried at room temperature for aperiod of from 2 to 10 minutes, preferably from 4 to 6 minutes.

The baking of the basecoat and topcoat films in stage (4) takes place insuitable apparatus known from the prior art, preferably at temperaturesbetween 120 and 160 degrees C, with particular preference between 130and 150 degrees C, for a period of preferably from 10 to 40 minutes,with particular preference from 15 to 30 minutes.

The present invention additionally provides a substrate coated with amulticoat finish, said finish being applied to the substrate surface by

(1): applying an aqueous basecoat A to the substrate surface,

(2): allowing the basecoat A applied in stage (1) to undergo evaporationto form a polymer film there-from,

(3): subsequently, applying an aqueous transparent topcoat B to thebasecoat film obtained in stage (2), and finally

(4): baking the basecoat film and the topcoat film together,

wherein the basecoat A comprises at least one hydroxyl-containing binderin aqueous solution or dispersion and a stable aqueous dispersion,prepared with a hydroxyl-containing emulsifier, of a hydrophobicizedamino resin.

Suitable substrates for coating are primarily pretreated metalsubstrates; however, it is also possible to cover nonpretreated metalsor any other substrates, such as wood or plastics, for example, with amulticoat protective and/or decorative coating using the basecoats ofthe invention.

The invention is illustrated using the following examples. All parts andpercentages are by weight unless expressly noted otherwise.

EXAMPLES Example 1

Preparation of an Aqueous Basecoat A1 of the Invention

In a reaction vessel with stirrer, internal thermometer, refluxcondenser and electrical heating, 237.4 g of a linear polyester(synthesized from dimerized fatty acid (Pripol® 1013), isophthalic acidand 1,6-hexanediol) having a hydroxyl number of 80 mg KOH/g and anumber-average molecular weight of 1400 are dissolved, following theaddition of 20.2 g of dimethylolpropionic acid and 7.2 g oftrimethylolpropane monoallyl ether, in 43.3 g of N-methylpyrrolidone and144.4 g of methyl ethyl ketone. Subsequently, 88.1 g of isophoronediisocyanate are added at 45° C. After the exothermic reaction hassubsided, the mixture is slowly heated to 80° C. It is maintained atthis temperature until the NCO content is 1.8%. Then, after cooling to50° C., 14.4 g of triethylamine and 538.5 g of deionized water are addedin rapid succession. After 15 minutes, a mixture of 7.3 g ofaminoethylethanolamine and 29.1 g of deionized water is added to thethoroughly dispersed resin. Subsequently, the temperature is raised to60° C. and the methyl ethyl ketone is distilled off under reducedpressure.

The resulting dispersion has a solids content of approximately 35% and apH of approximately 8.0.

463.2 g of the polyurethane resin dispersion prepared above are dilutedwith 263.7 g of deionized water. After the diluted dispersion has beenheated to 85° C., a mixture of 50.1 g of styrene, 50.1 g of methylmethacrylate, 37.5 g of n-butyl acrylate and 37.5 g of hydroxyethylmethacrylate is added slowly over the course of 3.5 hours. Beginning atthe same time as the addition of this mixture, a solution of 2.6 g oft-butyl perethylhexanoate in 35 g of methoxypropanol is added over thecourse of 4 hours. The mixture is subsequently held at 85° C. until themonomers have been fully consumed by reaction. If desired, furtherinitiator is added. Finally, any coagulum produced is removed byfiltration.

220 g of the thus-prepared dispersion of the acrylated polyurethaneresin are mixed, with stirring, with the following additional paintcomponents:

94.1 g of deionized water

160.0 g of polyacrylate dispersion Acronal® 290 from BASF

AG as further binder

1.0 g of ammonia

220.0 g of Laponite® as thickener

115.0 g of Aerosil® paste 805

40.0 g of Aerosil® paste 972

26.0 g of solution of a commercial wetting agent

90.0 g of a 3% strength solution of Viscalex® HV30 in water, asthickener

84.5 g of Irgazin® Red DPP BO (pigment)

26.5 g of Hostaperm® Pink E (pigment)

4.3 g of Bayferrox® 130 BM (pigment)

37.0 g of Novoperm® Orange (pigment)

6.2 g of titanium rutile (pigment) plus

55.4 g of an aqueous dispersion formed by mixing:

361.5 g of melamine resin Cymel® 1133

10.2 g of polyol emulsifier Pluronic® PE 9400, and

128.3 g of a buffer solution prepared by mixing 1.47 g oftriethanolamine, 0.45 g of formic acid and 126.4 g of deionized water.

Example 2

Preparation of an Aqueous Basecoat A2 of the Invention

The basecoat A2 is prepared as for Example 1 except that melamine resincomponent Resimene® X755 is used.

Example 3

Preparation of an Aqueous Basecoat A3 of the Invention

The basecoat A3 is prepared as for Example 1 except that melamine resincomponent Luwipal® 8792 is used.

Example 4

Preparation of an Aqueous Basecoat AC1

The basecoat AC1 as a comparative example is prepared as for Example 1except that melamine resin component Cymel® 1133 (40.0 g) is usedwithout emulsifier but together with an additional 19.5 g of deionizedwater.

Example 5

Producing a Two-Coat Paint System Using the Basecoats A1 to A3 of theInvention and, Respectively, the Comparative Example AC1

The basecoats prepared in accordance with Examples 1 to 4 are appliedusing a gravity-feed spray gun to a metal bodywork panel coated with acommercial electrodeposition coating material and a commercial filler,in such a way that the basecoat film, dried for 5 minutes at 20° C. andfor 10 minutes at 80° C., has a dry film thickness of about 15 μm. Thebasecoat film dried in this way is overcoated with an aqueous powderslurry clearcoat and baked at 130° C. for 30 minutes. The poppinglimits, mud-cracking limits and appearance measurements are set out inthe following table:

Test/basecoats A1 A2 A3 AC1 Popping limit μm 47 48 50 35 Mud-crackinglimit μm 48 49 50 48 Appearance Longwave 12 10 10 11 Shortwave 23 22 2322

What is claimed is:
 1. A process for applying a multicoat finish to asubstrate surface, comprising the steps of: (1) forming an aqueousbasecoat A by combining a dispersion of a hydrophobic amino resin in ahydroxyl containing emulsifier with an aqueous solution or dispersion ofa hydroxyl containing binder; (2) applying the aqueous basecoat A to thesubstrate surface; (3) forming a polymer film from the aqueous basecoatA applied in step 2; (4) applying an aqueous transparent topcoat B tothe basecoat film obtained in step (3); and (5) baking the basecoat filmand topcoat film together.
 2. The process as claimed in claim 1, whereinthe hydroxyl-containing emulsifier is a diol polyol or combinationsthereof.
 3. The process as claimed in claim 2, wherein thehydroxyl-containing emulsifier includes a diol or polyol having amolecular weight of at least 500 daltons.
 4. The process as claimed inclaim 2, wherein the hydroxyl-containing emulsifier comprises a memberselected from the group consisting of polyurethanediolspolyurethanepolyols, polycarbonatediols, polycarbonatepolyols,polyacrylatediols, polyacrylatepolyols, polyesterdiols,polyesterpolyols, polyetherdiols, polyetherpolyols, and combinationsthereof.
 5. The process as claimed in claim 4, wherein thehydroxyl-containing emulsifier comprises a polyurethanediol,polyurethanepolyol, polycarbonatediol, polycarbonatepolyol, orcombinations thereof.
 6. The process as claimed in claim 1, wherein thehydrophobic amino resin is a hydrophobic melamine resin.
 7. The processas claimed in claim 6, wherein the hydrophobic melamine resin isprepared by etherifying a melamine-formaldehyde condensate with C3 toC12 alcohols.
 8. The process as claimed in claim 1, wherein thehydroxyl-containing binder in the basecoat A is a polymer selected fromthe group consisting of polyacrylates, polyurethanes, polyesters,polyethers, alkyd resins cellulose derivatives, and combinationsthereof.
 9. The process as claimed in claim 8, wherein thehydroxyl-containing binder in the basecoat A is an aqueous dispersion ofan acrylated polyurethane resin.
 10. The process as claimed in claim 1,wherein the aqueous transparent topcoat B is an aqueous one-component ortwo-component clearcoat.
 11. The process as claimed in claim 10, whereinthe aqueous transparent topcoat B is a powder slurry clearcoat.
 12. Asubstrate coated with a multicoat finish, said finish being applied tothe substrate surface by a process comprising the steps of: forming anaqueous basecoat A by combining a dispersion of a hydrophobic aminoresin in a hydroxyl containing emulsifier with an aqueous solution ordispersion of a hydroxyl containing binder; (2) applying the aqueousbasecoat A to the substrate surface; (3) forming a polymer film from theaqueous basecoat A applied in step 2; (4) applying an aqueoustransparent topcoat B to the basecoat film obtained in step (3); and (5)baking the basecoat film and topcoat film together.
 13. The substrate ofclaim 12, wherein the hydroxyl-containing emulsifier is a diol, polyolor combinations thereof.
 14. The substrate of claim 13, wherein thehydroxyl-containing emulsifier comprises a member selected from thegroup consisting of polyurethanediols, polyurethanepolyols,polycarbonatediols, polycarbonatepolyols, polyacrylatediols,polyacrylatepolyols, polyesterdiols, polyesterpolyols, polyetherdiols,polyetherpolyols, and combinations thereof.
 15. The substrate of claim12, wherein the hydrophobic amino resin is a hydrophobic melamine resin.16. The substrate of claim 12, wherein the hydroxyl-containing binder inthe basecoat A is a polymer selected from the group consisting ofpolyacrylates, polyurethanes, polyesters, polyethers, alkyd resins,cellulose derivatives and combinations thereof.
 17. The substrate ofclaim 12, wherein the aqueous transparent topcoat B is an aqueousone-component or two-component clearcoat.
 18. The substrate of claim 17,wherein the aqueous transport topcoat B is a powder slurry clearcoat.